Banding may cause increase in penguin mortality rates

August 9, 2006

The banding of Adélie penguins for purposes of scientific research may increase mortality rates by as much as 13 percent. Photo: Katie Dugger, OSU Fisheries and Wildlife Department

CORVALLIS, Ore. – The banding of Adélie penguins for purposes of scientific research may increase mortality rates by as much as 13 percent, according to a new study reported in the July issue of The Auk, a quarterly journal of ornithology.

The study looked at populations of Adélie penguins in the western Ross Sea, Antarctica, over a period of four breeding seasons to determine whether or not flipper bands affected the ability of the flightless birds to forage for food and carry food loads. The study also looked at apparent annual survival rates for banded and unbanded birds.

The practice of banding birds has a long history in avian research and provides one of the most effective ways to monitor survival and dispersal of individuals over long periods of time, said Oregon State University’s Katie Dugger, lead author on the study and an expert in survival modeling. She is an assistant professor in the Fisheries and Wildlife Department in OSU’s College of Agricultural Sciences.

Because of penguins' unique body shape, leg bands, like those used on many other types of birds, are not a practical option for penguin research. Instead scientists band penguins on their upper flippers with small stainless steel bands about 0.1 cm thick that are resistant to pressure and temperature changes.

"This is the first study specifically aimed at studying the direct effects of bands on penguin foraging behavior and apparent survival," said Dugger. "For a survival study you need at least three years of banding data, and because of our unique project and its longevity we have eight years of data on banded birds and four years of data on birds that are not banded but have been implanted with radio-frequency identification (RFID) tags for comparison."

Penguin flipper bands are stamped with numbers that researchers can easily read through binoculars, eliminating the need for expensive technology or the recapturing of birds to aid in identification. They are also the only marking method that currently allows researchers to gather information on dispersal and age-related effects on apparent survival for Adélies, said Dugger.

However, she added, flipper bands may increase the amount of energy penguins must expend when foraging for the fish and krill in the Antarctic's frigid water.

In order to better understand the effect of the bands on the penguins, Dugger and her colleagues implanted a sample population of Adélies with tiny RFID tags that allowed them to use a scanner to passively monitor the birds as they traveled to and from the sea feeding their chicks.

The researchers then compared the foraging ecology and apparent survival between the RFID-marked birds and the banded birds to determine what effect, if any, flipper-bands were having on this species. They found that the bands significantly affected apparent survival of Adélie's, though the year-to-year survival of banded birds was highly variable. According to their study, from 2000-03 the bands appeared to decrease survival by 11-13 percent with males having a slightly higher rate of survival than females. However, when the researchers looked at data from banded birds over a longer time period they found that during certain years banded birds had levels of survivability of more than 90 percent. The duration of foraging trips was increased for banded birds, but the effect was relatively small and there were no differences in food loads between the two groups.

"What we seem to be finding is that in some years foraging effort is increased and survival is decreased for banded birds in comparison to unbanded birds," said Dugger. The researchers do not know exactly why the bands cause higher mortality, she added, but they are considering the possible effects on swimming efficiency, thermodynamics, and problems associated with ice accumulation around the bands during the winter.

Dugger said it is also possible that in years where winter and/or breeding season sea ice conditions are unfavorable, bands may increase the amount of energy required for foraging, and in turn decrease survival. In years with more favorable habitat conditions the bands may have no effect on survival.

"Most of us who band birds of any species want to think we're not doing any harm, but the truth is we usually don't know," said Dugger. "At some point the goal is to stop flipper-banding penguins, but for now we need to understand and balance the negative consequences of the bands with the beneficial gains in information from their use. Ultimately this kind of research may affect how we approach banding of all bird populations, not just penguins."

This study is part of a larger research project on Adélie penguin populations and their response to climate change. The project, now in its 11th year, is being conducted by researchers from OSU, PRBO Conservation Science, H.T. Harvey and Associates and Landcare Research New Zealand. It is funded by grants totaling more than $1.8 million from the National Science Foundation, the U.S. Antarctic Program and the New Zealand Antarctic Program.

Adélie penguins, which occur in large numbers in Antarctica, are considered an indicator species of environmental and fishery conditions, according to the Commission for the Conservation of Antarctic Marine Living.

"The health of Adélie populations is related to the pack ice, and patterns in the distribution and abundance of pack ice is changing as the earth's climate shifts," said Dugger, adding that the four years of the banding study that showed a decrease in apparent survival of banded birds corresponded to unusual sea ice conditions including the presence of a huge iceberg adjacent to the study colony that disrupted foraging and breeding of the Adélies.

For more information about this and other studies being conducted by this research team on Adélie penguins in the Antarctic, visit: http://www.penguinscience.com.